The Step-Current Annealing: An Easy Method to Improve the Magnetoimpedance in Co-Rich Ribbons

The magnetoimpedance (MI) response of Co-based amorphous ribbons, thermally treated by a dc step-current annealing, was studied. In this annealing method, a certain dc current value is passed through a ribbon at a fixed time, followed by a step-by-step increase in the current while also repeating the annealing. In this way, the growth of Co nanocrystalline grains on the surface of the ribbon slowly starts during the annealing. The nanocrystalline formation of Co layers on the surface was confirmed by X-ray diffraction patterns and field-emission scanning electron microscopy images. The current annealing under the optimum conditions of current and time leads to a higher induced anisotropy, thereby increasing the MI ratio. The step-current annealing is considered a simple and efficient technique to enhance the MI effect of amorphous ribbons, providing a tool for detecting weak magnetic fields at a relatively wider working range.